Electronic device for voltage switchable dielectric material having high aspect ratio particles

ABSTRACT

One or more embodiments provide for a device that utilizes voltage switchable dielectric material having semi-conductive or conductive materials that have a relatively high aspect ratio for purpose of enhancing mechanical and electrical characteristics of the VSD material on the device.

RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.12/703,701, filed Feb. 10, 2010, which:

-   -   (a) Is a Divisional of U.S. application Ser. No. 11/881,896,        filed Jul. 29, 2007, Issued as U.S. Pat. No. 7,695,644 on Apr.        13, 2010;    -   (b) Claims benefit of priority to Provisional U.S. Patent        Application No. 60/820,786, filed Jul. 29, 2006;    -   (c) Claims benefit of priority to Provisional U.S. Patent        Application No. 60/826,746, filed Sep. 24, 2006;    -   (d) Is a Continuation-In-Part of U.S. patent application Ser.        No. 11/562,289, filed Nov. 21, 2006; and    -   (e) Is a Continuation-In-Part of U.S. patent application Ser.        No. 11/562,222, filed Nov. 21, 2006; and        all of the aforementioned priority applications are hereby        incorporated by reference in their entirety.

TECHNICAL FIELD

The disclosed embodiments relate generally to the field of voltageswitchable dielectric (VSD) materials. More specifically, embodimentsdescribed herein include VSD material that includes conductive orsemi-conductive high aspect-ratio (HAR) particles as filler.

BACKGROUND

Voltage switchable dielectric (VSD) material has an increasing number ofapplications. These include its use on, for example, printed circuitboards and device packages, for purpose of handling transient voltagesand electrostatic discharge events (ESD).

Various kinds of conventional VSDM exist. Examples of voltage switchabledielectric materials are provided in references such as U.S. Pat. No.4,977,357, U.S. Pat. No. 5,068,634, U.S. Pat. No. 5,099,380, U.S. Pat.No. 5,142,263, U.S. Pat. No. 5,189,387, U.S. Pat. No. 5,248,517, U.S.Pat. No. 5,807,509, WO 96/02924, and WO 97/26665. VSD material can be“SURGX” material manufactured by the SURGX CORPORATION (which is ownedby Littlefuse Inc.).

While VSD material has many uses and applications, conventionalcompositions of the material have had many shortcomings. Typicalconventional VSD materials are brittle, prone to scratching or othersurface damage, lack adhesive strength, and have a high degree ofthermal expansion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating components for use in a processof formulating VSD material, according to an embodiment of theinvention.

FIG. 2 illustrates a process for formulating a composition of VSDmaterial having high aspect ratio particles in a binder, under anembodiment of the invention.

FIG. 3A is a cross-sectional illustration of VSD material, where the VSDmaterial is formulated in accordance with one or more embodiments of theinvention.

FIG. 3B illustrates a graph of basic electrical properties of clamp andtrigger voltage for VSD material, in accordance with embodiments such asdescribed with FIG. 3A and elsewhere.

FIG. 3C-FIG. 3E illustrate voltage by current performance graphs ofdifferent examples of VSD material, responding to the occurrence ofvoltage events, under one or more embodiments of the invention.

FIG. 4 illustrates another process by which VSD material may include HARparticles for coating conductors or semi-conductor particles, under anembodiment of the invention.

FIG. 5A and FIG. 5B illustrate how application of HAR particles to coatthe surface of the metal/inorganic conductor or semiconductor particlescan reduce the loading of such particles in the VSD material, under anembodiment of the invention.

FIG. 5C illustrates a relatively disorganized distribution of HARparticles as fillers in a binder of VSD material, when such particlesare dispersed at nanoscale in the binder, according to an embodiment ofthe invention.

FIG. 6A and FIG. 6B each illustrate different configurations for asubstrate device that is configured with VSD material having HARparticles distributed in its binder, under an embodiment of theinvention.

FIG. 7 illustrates a process for electroplating, using organic VSDmaterial in accordance with any of the embodiments described with FIG.1-5C.

FIG. 8 is a simplified diagram of an electronic device on which VSDmaterial in accordance with embodiments described herein may beprovided.

DETAILED DESCRIPTION

Embodiments described herein provide for devices that incorporate acomposition of VSD material that utilizes semi-conductive or conductivematerials that have a relatively high aspect ratio for purpose ofenhancing mechanical and electrical characteristics of the VSD material.Still further, other embodiments contemplate use of nanoscale conductorsand semiconductors for use in enhancing the properties andcharacteristics of VSD material.

In general, “voltage switchable material” or “VSD material” is anycomposition, or combination of compositions, that has a characteristicof being dielectric or non-conductive, unless a voltage is applied tothe material that exceeds a characteristic voltage level of thematerial, in which case the material becomes conductive. Thus, VSDmaterial is a dielectric unless voltage exceeding the characteristiclevel (e.g. such as provided by ESD events) is applied to the material,in which case the VSD material is conductive. VSD material can furtherbe characterized as any material that can be characterized as anonlinear resistance material.

VSD material may also be characterized as being non-layered and uniformin its composition, while exhibiting electrical characteristics asstated.

Still further, an embodiment provides that VSD material may becharacterized as material comprising a binder mixed in part withconductor or semi-conductor particles. In the absence of voltageexceeding a characteristic voltage level, the material as a whole adaptsthe dielectric characteristic of the binder. With application of voltageexceeding the characteristic level, the material as a whole adaptsconductive characteristics.

As will be described, one or more embodiments provide for HAR particlesto be combined in the binder of the VSD material. The HAR particles maybe dispersed as nanoscale particles within the binder to enablereduction of metal loading, enhancement of mechanical properties, and/orimproved electrical performance, as compared to more conventional VSDmaterials.

Among other advantages, embodiments described herein provide for devicesthat incorporate, integrate or otherwise provide a composition of VSDmaterial that has improved mechanical properties, including propertiesof high compression strength, scratch resistance and non-brittleness.Additionally, one or more embodiments described herein provide forformulation of VSD material that has high adhesive strength and goodability to adhere to metals such as copper. Numerous other advantagesmay also be provided with compositions such as described.

Accordingly, one or more embodiments further include a binder for a VSDcomposition that includes “nanoscale” dimensioned conductive orsemi-conductive particles. These may include HAR particles, and in somecases super HAR particles (having aspect ratios of the order of 1000 ormore). In this application, nanoscale particles are particles for whicha smallest dimension (e.g. diameter or cross-section) is less than 500nanometers. One or more embodiments contemplate nanoscale particleshaving a smallest dimension that is less than 100 nm, and still further,other embodiments contemplate a dimension that is less than 50 nm.Examples of such particles include carbon nanotubes, although numerousother kinds of particles are contemplated. Carbon nanotubes are examplesof super HAR particles, with aspect ratios of an order of 1000:1 andmore. Materials with lesser aspect ratios are also contemplated as analternative or addition to carbon nanotubes, including one or more ofcarbon black (L/D of order of 10:1) particles and carbon fiber (L/D ofan order of 100:1) particles.

Still further, alternative embodiments contemplate use of nanoscaleparticles that have moderate aspect ratios. For example, one or moreembodiments include combining nanorods with the binder of the VSDmaterial. Some variations of nanorods, formed from metals orsemiconductors, have aspect ratios that range between 3-10 nm. Thus, oneor more embodiments contemplate use of nanoscale conductors orsemiconductors that have moderate aspect ratios.

The amount of such polymer phase particles that may occupy the VSDmaterial is selected so that the VSD remains below (or just below) thepercolation threshold. To maintain the VSD material at below thepercolation threshold, the amount of metal particles (or othernon-polymer phase particles) used in the VSD composition may vary inconnection with the amount of polymer particles used. Thus, according toone or more embodiments, the amount of metal particles that can be usedto formulate the VSD may be affected slightly (or otherwise) by theamount of (semi-) conductive materials used in the polymer of the VSDcomposition, so that the material as a whole remains at just below thepercolation threshold.

As mentioned, the amount of HAR particles that can be used may beoptimized or limited by the electrical characteristic of the VSDmaterial as a whole. In one embodiment, the amount and type of HARparticles may be set to an amount that causes the binder of the VSDmaterial to be just at or below its percolation threshold. In order toprovide for the binder to be at this limit, the amount of metalparticles that also comprise the VSD material may be adjusted, dependingon design parameters and characteristics desired from the VSD.

This enhanced current handling capacity allows for the ability to handlelarger energy events than previous ESD materials. Examples of thesetypes of events would be ESD, EFT, EOS and lightning.

Generally, the characteristic voltage of VSD material is measured atvolts/length (e.g. per 5 mil). One or more embodiments provide that theVSD material has a characteristic voltage level that exceeds that of anoperating circuit. Such voltage levels may be associated with transientconditions, like electrostatic discharge, although embodimentscontemplate planned electrical events. Furthermore, one or moreembodiments provide that in the absence of the voltage exceeding thecharacteristic voltage, the material behaves similar to the binder.

Still further, an embodiment provides for VSD material formed from thestated process or method.

Still further, an electronic device may be provided with VSD material inaccordance with any of the embodiments described herein.

In an embodiment, the HAR particle or material is single or multi-walledcarbon nanotube.

Furthermore, one or more embodiments provide material that is uniformlymixed and/or non-layered material across a cross-section. Such materialmay be VSD in that it exhibit non-ohmic characteristics, such as theability to switch from being a dielectric to a conductor with theapplication of a voltage that exceeds the characteristic voltage.

FIG. 1 is a block diagram illustrating components for use in a processof formulating VSD material, according to embodiments of the invention.In an embodiment, conductive (and/or) semi-conductive high aspect-ratio(HAR) particles 110 are combined with conductor and/or semi-conductorparticles 120 to form VSD material 140. As an optional addition,insulator particles may also be combined with theconductor/semiconductor particles 120. Binder 130 may be combined withthe HAR particles 110 and the conductive particles to form the VSDmaterial 140. A VSD formulation process 150 may be used to combine thevarious ingredients of the VSD material 140. Formulation processes foruse of VSD material HAR particles 110 are described below, with, forexample, an embodiment of FIG. 2.

In one embodiment, the binder 130 is a matrix that retains the HARparticles 110 and the conductor/semi-conductor particles 120. In oneembodiment, the HAR particles 110 are dispersed as nanoscale particles.In one embodiment, the amount of HAR particles that are dispersed in thebinder place the binder at just below the percolation threshold. Asdispersed nanoscale particles, the HAR particles 110 include particlesthat are both nanoscaled in one or more dimensions (e.g. cross-section,diameter, width) and individually separated from one another. Thus, theformulation process 150 may uniformly distribute the particles withinthe binder 130.

In one embodiment, HAR particles 110 include organic conductive orsemi-conductive particles, and in particular elongated particles thatare carbon-only. For example, HAR particles 110 may correspond toelongated or cylindrical fullerenes, including carbon nanotubes or evencarbon black. The carbon nanotubes may be a single or multi-wallvariety.

As an addition or alternative, HAR particles 110 may correspond toconductive or semi-conductive inorganic particles, such as provided bynanowires or certain types of nanorods. Material for such particlesinclude copper, nickel, gold, silver, cobalt, zinc oxide, tin oxide,silicon carbide, gallium arsenide, aluminum oxide, aluminum nitride,titanium dioxide, antimony, boron nitride, tin oxide, indium tin oxide,indium zinc oxide, bismuth oxide, cerium oxide, and antimony zinc oxide.

In an embodiment, the conductor/semi-conductor particles 120 includeconductors such as metals, in combination with semiconductor particlesthat include silicon, silicon carbide, titanium dioxide, boron nitride,aluminum nitride, nickel oxide, zinc oxide, zinc sulfide, bismuth oxide,cerium oxide, iron oxide, metal or/and complexes selected from a groupconsisting of oxides, metal nitrides, metal carbides, metal borides,metal sulfides, or a combination thereof.

According to one or more embodiments, other ingredients or componentsfor use in the formation process 150 include solvents and catalysts.Solvents may be added to the binder 130 to separate particles that wouldotherwise be lumped or agglomerated at nanoscale. A mixing process mayalso be used to uniformly space separated particles. In one embodiment,the result of the mixing process is that the composition is uniformlymixed to disperse particles at the nanoscale. Thus, particles such ascarbon nanotubes or other HAR particles may be separated outindividually and distributed relatively evenly in the material. In orderto achieve nanoscale dispersion, one or more embodiments provide for useof sonic agitators and sophisticated mixing equipment (e.g. such asrotor-stator mixers, ball mills, mini-mills, and other high shear mixingtechnologies), over a duration that lasts several hours or longer. Oncemixed, the resulting mixture may be cured or dried.

The binder 130 may also be of various types. The binder 130 may beprovided in the form of a binder that retains the HAR particles 110 andthe conductor/semi-conductor particles 120. According to differentembodiments, the binder 130 is formed from a material selected from agroup consisting of silicone polymers, phenolic resins, epoxy, phenolicresin, polyurethane, poly(meth)acrylate, polyamide, polyester,polycarbonate, polyacrylamides, polyimide, polyethylene, polypropylene,polyphenylene oxide, polysulphone, solgel materials, and ceramers. Thebinder 130 may correspond to a binder that suspends and/or retains theHAR particles 110, conductor/semi-conductor particles 120, as well asother particles or compounds that comprise the VSD material 140.

VSD Formulation with HAR Material

Broadly, embodiments provide for use of VSD material that includes, bypercentage of volume, 5-99% binder, 0-70% conductor, 0-90%semiconductor, and HAR material that is conductive or semi-conductiveand having a volume of composition in a range of 0.01-95%. One or moreembodiments provide for use of VSD material that includes, by percentageof volume, 20 to 80% binder, 10 to 50% conductor, 0% to 70%semiconductor, and HAR material that is conductive or semi-conductiveand having a volume of the composition in a range of 0.01-40%. Stillfurther, one or more embodiments provide for use of VSD material thatincludes, by percentage of volume, 30 to 70% binder, 15 to 45%conductor, 0% to 50% semiconductor, and HAR material that is conductiveor semi-conductive and having a volume of the composition in a range of0.01-25%. Examples of binder materials include silicone polymers, epoxy,polyimide, phenolic resins, polyethylene, polypropylene, polyphenyleneoxide, polysulphone, solgel materials, ceramers, and inorganic polymers.Examples of conductive materials include metals such as copper,aluminum, nickel, silver, gold, titanium, stainless steel, chrome, andother metal alloys. Examples of semiconductive material include bothorganic and inorganic semiconductors. Some inorganic semiconductorsinclude silicon, silicon carbide, boron nitride, aluminum nitride,nickel oxide, zinc oxide, zinc sulfide, bismuth oxide, and iron oxide.The specific formulation and composition may be selected for mechanicaland electrical properties that best suit the particular application ofthe VSD material.

FIG. 2 illustrates a process for formulating a composition of VSDmaterial having HAR material, according to an embodiment of theinvention. Initially, in a step 210, a resin mixture is createdcontaining a combination of conductor and semi-conductor particles, aswell as HAR particles that serve as fillers to reduceconductor/semiconductor particle composition in the binder. The resinmixture may serve as the binder of the VSD material when formulation iscomplete. In one embodiment, the HAR particles may correspond to carbonnanotubes. Other embodiments provide for use of nanowires or nanorods.

According to one embodiment, the amount of HAR particles added to themixture is designated to maintain the mixture as a whole at just belowpercolation threshold. However, the amount of HAR particles that arepresent may vary, depending on the desired percentage by volume of theparticles in the formulated VSD material. In one embodiment in whichcarbon nanotubes are used as the HAR particles, the quantity of carbonnanotubes added to the resin results in carbon nanotubes having apercentage by weight of less than 10% of the overall composition, andmore specifically between 0.1% and 10% of the formulated VSD material.Embodiments described herein recognize that the amount of HAR particlesused in the binder to achieve a desired effect may depend on the aspectratio of the material being considered. For example, the binder mayinclude more than 10% HAR particles if the aspect ratio of theindividual HAR particles is relatively low. As a more specific example,particles with aspect ratios of 1000:1 may occupy 1% by weight of theoverall material, while particles with individual aspect ratios of 10:1may require 25% or more.

In step 220, metallic and/or inorganic conductors/semiconductors areadded to the mixture. As described with an embodiment of FIG. 1,numerous types of conductors or semi-conductors may be used. More thanone kind of organic/semiconductor particle may be added. In oneembodiment, Titanium dioxide (TiO₂) is used as the (or one of the)primary types of conductive/semiconductive particles, along withadditional conductor particles. Additional curative and catalystconstituents may also be added to the mixture.

In step 230, a mixing process may be performed over a designatedduration. In one embodiment, the mixing process is performed with mixingequipment, including sonic agitators, for a duration that that extendsfor minutes or hours. The mixing process serves to disperse the HARparticles at a nanoscale level. One result of mixing to such degree isthat at least some of the HAR particles are substantially suspendedapart from one another within the binder, so as to not agglomerated orlumped together. Given that the HAR particles individually may includeone or more dimensions at the nanoscale, such mixing further enablesnanoscale dispersion within the binder.

In step 240, the mixture is applied to its desired target. For example,the mixture may be applied to across a 5 mil gap between two givenelectrodes of a particular device. At the target location, the mixtureis cured into VSD material.

As described with an embodiment of FIG. 1, the resulting VSD materialhas numerous improved mechanical properties over more conventional VSDmaterial. For example, among other improvements that may result, the VSDmaterial formulated in accordance with an embodiment such as describedmay be less brittle, have better compression strength, adhere better tometals (particularly copper), and/or have better aesthetic properties.

Example Formulation and Composition

A compound in accordance with embodiments described herein may beformulated as follows: HAR particles may be provided in the form ofcarbon nanotubes (CNT), which are added to a suitable resin mixture. Inone embodiment, the resin mixture includes Epon 828 and a silanecoupling agent. NMP (N-methyl-2pyrrolidone) may be added to the resinmixture. Subsequently, conductor or semiconductor particles may be addedto the mixture. In one embodiment, titanium dioxide is mixed into theresin, along with titanium nitride, titanium diboride, a curativecompound or agent, and a catalyst agent. The mixture may be uniformlymixed for a mixing duration that lasts hours (e.g. 8 hours) using, forexample, rotor-stator mixer with sonication. NMP may be added asnecessary for the mixing duration. The resulting mixture may be appliedas a coating using #50 wire wound rod or screen print on a desiredtarget. In one embodiment, the coating may be applied across a 5 mil gapbetween 2 electrodes. Subsequently, a cure process may take place thatmay be varied. One suitable curing process includes curing for tenminutes at 75 C, ten minutes at 125 C, 45 minutes at 175 C, and 30minutes at 187 C.

Specific formulations may vary based on design criteria and application.One example of a formulation in which carbon nanotubes are used HARparticles of the binder of the VSD material include:

Weight (g) CheapTubes 5.4 Epon 828 100 Gelest Aminopropyltriethoxysilane4 Total Epoxy 104 Nanophase Bismuth Oxide 98 HC Starck TiN— 164 DegussaDyhard T03 4.575 NMP 25.925 Curative Soln. 30.5 1-methylimidazole 0.6 HCStark TiB2— 149 Millenium Chemical Doped TiO2— 190 NMP 250 TotalSolution 986.1 Total Solids 715.575 Epoxy:Amin Equiv Ratio % Solids72.6% *Curative Solution is a 15% by weight solution of Dyhard T03dissolved in NMP.

Carbon nanotubes have the benefit of being organic filler. The lengthsor aspect ratios may be varied to achieve a desired property, such asswitching voltage for the material.

FIG. 3A is a cross-sectional illustration of VSD material provided on adevice 302, where the VSD material is formulated in accordance with oneor more embodiments of the invention. In an embodiment, a thickness orlayer or VSD material 300 includes basic constituents of metal particles310, binder material 315, and HAR particles 320 (e.g. carbon nanotubes,nanowires).

Embodiments recognize, however, that carbon nanotubes have considerablelength to width ratio. This dimensional property enables carbonnanotubes to enhance the ability of the binder to pass electrons fromconductive particle to conductive particle in the occurrence of atransient voltage that exceeds the characteristic voltage. In this way,carbon nanotubes can reduce the amount of metal loading present in theVSD material. By reducing the metal loading, physical characteristics ofthe layer may be improved. For example, as mentioned with one or moreother embodiments, the reduction of metal loading reduces thebrittleness of the VSD material 300.

As described with an embodiment of FIG. 2, the VSD material 300 may beformed on device 302 by being deposited as a mixture on a targetlocation of the device 302. The target location may correspond to a span312 between a first and second electrode 322, 324. According to one ormore embodiments, the span 312 is about (i.e. within 60%) 3.0 mil, 5.0mil, or 7.5 mil for applications such as printed circuit boards.However, the exact distance of the span 312 may vary based on designspecification. In PCB applications, the range may vary, for example,between 2 and 10 mils. In semi-conductor packages, the value may be muchless. Application of the VSD material in the gap enables handling ofcurrent that result from transient voltages that exceed thecharacteristic voltage of the VSD material.

Device 302 may be used with any one of many kinds of electrical devices.In an embodiment, device 302 may be implemented as part of a printedcircuit board. For example, the VSD material 300 may be provided as athickness that is on the surface of the board, or within the board'sthickness. Device 302 may further be provided as part of asemi-conductor package, or discrete device.

Alternatively, device 302 may correspond to, for example, alight-emitting diode, a radio-frequency tag or device, or asemiconductor package.

As described with other embodiments, VSD material, when applied to atarget location of a device, may be characterized by electricalproperties such as characteristic (or trigger) voltage, clamp voltage,leakage current and current carrying capacity. Embodiments describedherein provide for use of HAR particles in a mixture that enablesadjustment of electrical properties such as described, while maintainingseveral desired mechanical properties described elsewhere in thisapplication.

FIG. 3B illustrates a graph of basic electrical properties of clamp andtrigger voltage for VSD material, in accordance with embodiments such asdescribed with FIG. 3A and elsewhere in this application. Generally, thecharacteristic or trigger voltage is the voltage level (which may varyper unit length) by which the VSD material turns on or becomesconductive. The clamp voltage is typically less than or equal to thetrigger voltage and is the voltage required to maintain the VSD materialin the on-state. In some cases when the VSD material is provided betweentwo or more electrodes, the trigger and clamp voltages may be measuredas output across the VSD material itself. Thus, the on-state of the VSDmaterial may be maintained by maintaining the input voltage level atabove the clamp voltage, for a duration that is less than the break downthreshold energy or time. In application, the trigger and/or clampvoltages may be varied as a result of an input signal that is spiked,pulsed, shaped or even modulated over several pulses.

Embodiments further recognize that another electrical property ofinterest includes off-state resistance, determined by measuring currentthrough operational voltages of the device. The resistivity of theoff-state may correspond to the leakage current. A change in off-stateresistivity as compared to before and after when the VSD material isturned on and off signals degradation of the performance of the VSDmaterial. In most cases, this should be minimized.

Still further, another electrical characteristic may correspond tocurrent carrying capacity, measured as the ability of the material tosustain itself after being turned on, then off.

Table 1 lists another formulation of VSD material, in which the HARparticle used in the binder is antimony tin oxide (ATO) Nanorods, inaccordance with one or more embodiments.

Material Example 1 Ishihara Corp FS-10P ATO nanorods 14.4 HC Starck TiB2150.0 Gelest SIA610.1 4.0 Millenium Chemical TiO2 190.0 Lubrizole D5109.8 Nanophase Bi2O3 98.0 HC Starck TiN 164.0 Epon 828 (Hexion) 87.15Degussa Dyhard T03 4.49 1-methylimidazole 0.62 N-methylpyrrolidinone275.4 Gap 5 mil Trigger Voltage 447 Clamp Voltage 320Table 2 lists several additional examples in which the VSD material iscomposed of carbon nanotubes as the HAR particles in accordance with oneor more embodiments described herein. Table 2 lists generically measuredelectrical properties (meaning no differentiation is provided betweenforms of input signal and/or manner in which data for electricalproperties is determined), as quantified by clamp and trigger voltagesthat result from use of the VSD material in accordance with the statedcomposition.

TABLE 2 Example 1 Example 2 Example 3 Example 4 Material Weight (g)Weight (g) Weight (g) Weight (g) Hyperion CP-1203 0 31.29 0 40.86 NickelINP400 216.27 221.49 0 0 Momentive TiB2 0 0 55.36 55.4 (formerly GE)Saint Gobain BN 0 0 0 0 Epon 828 (Hexion) 40.13 10.09 51.06 12.18Degussa Dyhard T03 1.83 1.83 2.34 2.33 1-methylimidazole 0.1 0.13 0.30.3 imidazoledicarbonitrile 0 0 0 0 Methylaminoantracene 0 0 0 0Millenium Chemical 0 0 85.03 85.79 TiO2 N-methylpyrrolidinone 80.3780.46 83.5 123.4 Gap 5 mil 5 mil 5 mil 5 mil Trigger Voltage 250 1701475 775 Clamp Voltage 100 70 1380 220

With respect to Table 2, Example 1 provides a composition of VSDmaterial that is a basis for comparison with other examples. In Example1, HAR particles are not present in the VSD material. Furthermore, theVSD material has relatively high metal loading. Example 2 illustrates asimilar composition as to Example 1, but with the introduction of carbonnanotubes as the HAR particles. The result is a reduction in trigger andclamp voltage. Trigger and clamp voltages are reduced by adding carbonnanotubes at a given (constant) nickel loading.

Example 3 also illustrates a VSD composition that lacks carbon nanotubesas HAR particles, while Example 4 illustrates effect of including carbonnanotubes into the mixture. As shown, a dramatic reduction in thetrigger and clamp voltages is shown. With regard to Example 3 andExample 4, both compositions illustrate compositions that have desirablemechanical characteristics, as well as characteristics of off-stateresitivity and current-carrying capacity (neither of which arereferenced in the chart). However, the clamp and trigger voltage valuesof Example 3 illustrate the composition, without inclusion of carbonnanotubes, is difficult to turn on and maintain on. Abnormally hightrigger and clamp voltages thus reduce the usefulness of thecomposition.

The performance diagrams shown with FIG. 3C-3E assume pulsed voltageinputs. The performance diagrams may be referenced to the examplesprovided in the following table.

TABLE 3 Example 5 Example 6 Example 7 Material Weight (g) Weight (g)Weight (g) Hyperion CP1203 21.0 0 1.0 Hexion Epon 828 50.25 0 5 Cabosilcoated Aluminum 40.33 26.33 0 ATA5669 aluminum 0 0 13.76 Degussa DyhardT03 3.22 0.8 0.6 Methoxyethanol 25.8 6.39 4.68 1-methylimidazole 0.060.04 0.04 Hexion Epon SU-8 0 19.55 14.32 Methyl ethyl ketone 0 11.73 6.6Cabosil coated Alumina 0 15.31 0

FIG. 3C is a diagram that illustrates a performance diagram for VSDmaterial that has a relatively large quantity of concentration of carbonnanotubes (as HAR particles) in the binder of the VSD material, asdescribed by Example 5. As shown by the diagram of FIG. 3C, theoccurrence of an initial voltage event 372 in the range of 500-1000volts results in the material turning on, so as to carry current.Application of a second voltage event 374 after the device turns offfrom the first event results in a similar effect as the initial event372, in the material carries currents at relatively the same voltagelevels. The occurrence of the third voltage event 376 after the deviceturns off the second time results in a similar result in the amperagecarried in the VSD material as the first two occurrences. As such FIG.3C illustrates the VSD material of the composition in Example 5 hasrelatively-high current carrying capacity, in that the VSD materialremains effective after two instances of switching on and off.

FIG. 3D correlates to Example 6, which is a VSD composition thatcontains no conductive or semi-conductive organic material. While theVSD material is effective in the first voltage event 382, there is nodetectable non-linear behavior (i.e. turn-on voltage) when thesubsequent second voltage event 384 occurs.

FIG. 3E correlates to Example 7, which has fewer amount of HAR particlesin the form of carbon nanotubes. The light addition of suchconductive/semi-conductive HAR particles improves the current carryingcapacity of the VSD material, as shown by the amperage of the firstvoltage event 392 and the lesser (but present) amperage of the secondvoltage event 394.

Coated Conductive or Semi-Conductive Particles

One or more embodiments include a formulation of VSD material thatincludes the use of conductive or semi-conductive HAR particlemicro-fillers that are coated or otherwise combined onto a periphery ofa metal particle. Such formulation allows for additional reduction inthe size of the metal particle and/or volume that would otherwise beoccupied by the metal particle. Such reduction may improve the overallphysical characteristics of the VSD material, in a manner described withother embodiments.

As described below, one or more embodiments provide for the use of HARparticle micro-fillers that coat or bond metal or other inorganicconductor elements. One objective of coating the inorganic/metalparticles with HAR particles is to generally maintain overall effectivevolume of the conductive material in the binder of the VSD material,while reducing a volume of metal particles in use.

FIG. 4 illustrates a more detailed process by which VSD material can beformulated, under an embodiment of the invention. According to a step410, the conductive elements (or semi-conductive) that are to be loadedinto a binder for VSD formulation are initially prepared. This step mayinclude combining HAR particles (e.g. carbon nanotubes) with particlesthat are to be coated so as to create a desired effect when the endmixture is cured.

In one implementation, separate preparation steps are performed for themetal and metal oxide particles. Under one embodiment, step 410 mayinclude sub-steps of filtering aluminum and alumina powder. Each of thepowder sets are then coated with HAR particles to form theconductive/semi-conductive element. In one implementation, the followingprocess may be used for aluminum: (i) add 1-2 millimole of silane pergram of Aluminum (dispersed in an organic solvent); (ii) apply sonicapplicator to distribute particles; (iii) let react 24 hours withstirring; (iv) weigh out Cab-O-Sil or organic conductor into solution;(v) add suitable solvent to Cab-O-Sil or organic conductor mix; (vi) addCab-O-Sil and/or organic conductor to collection with Aluminum; and(vii) dry overnight at 30-50 C.

Similarly, the following process may be used by used for the Alumina:(i) add 1-2 millimole of silane per gram of Alumina (dispersed in anorganic solvent); (ii) apply sonic applicator to distribute particles;(iii) let react 24 hours with stirring; (iv) weigh out Cab-O-Sil ororganic conductor into solution; (v) add Cab-O-Sil and/or organicconductor to collection with Alumina; (vi) dry overnight at 30-50 C.

According to an embodiment, HAR particles such as carbon nanotubes ornanowires may be used in coating or preparing the conductive elements.The carbon nanotubes may be biased to stand on end when bonded with themetal particles, so as to extend conductive length of the particles,while at the same time reducing the overall volume of metal needed. Thismay be accomplished by placing a chemical reactive agent on the surfaceperimeter of the metal particles that are to form conductors within theVSD material. In one embodiment, the metal particles may be treated witha chemical that is reactive to another chemical that is positioned atthe longitudinal end of the HAR particle (e.g. carbon nanotube). Themetal particles may be treated with, for example, a Silane couplingagent. The ends of the HAR particles may be treated with the reactiveagent, to enable end-wise bonding of the carbon nano-tubes to thesurface of the metal particles.

In step 420, a mixture is prepared. Binder material may be dissolved inan appropriate solvent. Desired viscosity may be achieved by adding moreor less solvent. The conductive elements (or semi-conductive elementsfrom step 410) are added to the binder materials. The solution may bemixed to form uniform distribution. Appropriate curative may then beadded.

In step 430, the solution from step 420 is integrated or provided onto atarget application (i.e. a substrate, or discrete element or a LightEmitting Diode or Organic LED), then heated or cured to form a solid VSDmaterial. Prior to heating, the VSD material may be shaped or coated forthe particular application of the VSD material. Various applications forVSD material with HAR particle coating or bonding with metallic orinorganic conductors/semiconductors exist.

FIG. 5A and FIG. 5B illustrate how application of HAR particles to coator bind the surface of the metal/inorganic conductor or semiconductorscan reduce loading of such particles, under an embodiment of theinvention. FIG. 5A is a simplified illustration of how conductor and/orsemiconductor particles in a binder of the VSD material can be surfacecoated with carbon nanotubes. As shown, conductive element 500 includesa metal particle 510 and a metal oxide or other optional inorganicsemi-conductor particle 520. The metal particle 510 may have a dimensionrepresented by a diameter d1, while the metal oxide particle 520 mayhave a dimension represented by d2. In an embodiment shown by FIG. 5A,HAR particle fillers 530 (e.g. carbon nanotubes) are bonded or combinedwith a periphery of the respective particles 510, 520. As the HARparticle fillers 530 are conductive or semi-conductive, the effect is toincrease the size of the particles 510, 520 without increasing thevolume of those particles in the binder of the VSD material. Thepresence of the HAR particle fillers enables conduction, or electronhopping or tunneling from molecule to molecule when voltage exceedingthe characteristic voltage occurs. The conductive element 500 may infact be semi-conductive, in that conductive element 500 may have theproperty of being collectively conductive when a characteristic voltageis exceeded.

In FIG. 5B, a conventional VSD material is shown without addition of HARparticles. Metal particles 510, 520 are relatively closely spaced inorder to pass charge when voltage exceeding the characteristic voltageis applied. As a result of more closely spaced conductors, more metalloading is required to enable the device to switch to a conductor state.In comparison to an embodiment such as illustrated by FIG. 5A, under aconventional approach shown by FIG. 5B, the particles 510, 520 arespaced by glass particle spaces (e.g. Cab-O-Sil), an embodiment such asshown in FIG. 5A substitutes metal volume with conductive fillers 530that are conductive, have desirable physical properties, and havedimensions to adequately substitute for metal.

FIG. 5C illustrates a relatively disorganized distribution of HARparticle fillers (e.g. carbon nanotubes), reflecting how the HARparticle fillers, when uniformly dispersed at nanoscale, inherentlyproduce results that are similar to those desired from the simplifiedillustration of FIG. 5A. A description of FIG. 5C may reflectembodiments such as shown and described with FIG. 3 or elsewhere in thisapplication. As shown, a number of uniformly distributedconductive/semi-conductive HAR particle fillers 530 enables sufficienttouching and/or proximity to enable a conductive path for handlingcurrent, including through electron tunneling and hopping. This allowsimprovement in electrical and physical characteristics, particularly inrelation to reduction of metal loading in the binder of the VSDmaterial. Moreover, when particles are evenly dispersed at nanoscalewithin the binder, less HAR particle 530 is needed to produce thedesired electrical conductivity effect.

VSD Material Applications

Numerous applications exist for VSD material in accordance with any ofthe embodiments described herein. In particular, embodiments provide forVSD material to be provided on substrate devices, such as printedcircuit boards, semiconductor packages, discrete devices, as well asmore specific applications such as LEDs and radio-frequency devices(e.g. RFID tags). Still further, other applications may provide for useof VSD material such as described herein with a liquid crystal display,organic light emissive display, electrochromic display, electrophoreticdisplay, or back plane driver for such devices. The purpose forincluding the VSD material may be to enhance handling of transient andovervoltage conditions, such as may arise with ESD events. Anotherapplication for VSD material includes metal deposition, as described inU.S. Pat. No. 6,797,145 to L. Kosowsky (which is hereby incorporated byreference in its entirety).

FIG. 6A and FIG. 6B each illustrate different configurations for asubstrate device that is configured with VSD material having highaspect-ratio particles as filler (“HAR particled VSD”), under anembodiment of the invention. In FIG. 6A, the substrate device 600 maycorrespond to, for example, a printed circuit board. In such aconfiguration, HAR particled VSD 610 may be provided on a surface 602 toground a connected element. As an alternative or variation, FIG. 6Billustrates a configuration in which the HAR particled VSD forms agrounding path within a thickness 610 of the substrate.

Electroplating

In addition to inclusion of the VSD material on devices for handling,for example, ESD events, one or more embodiments contemplate use of VSDmaterial to form substrate devices, including trace elements onsubstrates, and interconnect elements such as vias. U.S. Pat. No.6,797,145 (incorporated herein in its entirety) recites numeroustechniques for electroplating substrates, vias and other devices usingVSD material. Embodiments described herein enable use of HAR particledVSD material, as described with any of the embodiments in thisapplication.

FIG. 7 illustrates a process for electroplating, using HAR particled VSDmaterial in accordance with any of the embodiments described with FIG.1-5. The enhanced physical and electrical properties provided byembodiments described herein facilitate electroplating processes such asdescribed in U.S. Pat. No. 6,797,145. FIG. 7 describes a simplifiedelectroplating process, such as described in U.S. Pat. No. 6,797,145, inwhich the VSD material used is in accordance with any of the embodimentsdescribed with FIG. 1 thru FIG. 5.

In FIG. 7, a basic electroplating technique is described, according toone or more embodiments of the invention. In a step 710, a target regionof a device (e.g. a substrate) is patterned using HAR particled VSDmaterial. The patterning may be performed by, for example, applying acontinuous layer of VSD over a substrate, then placing a mask over theVSD layer. The mask may define the negative pattern of the desiredelectrical/trace pattern. Alternatives are also possible. For example,the VSD material may be applied to the entire region, and thenselectively removed to expose regions that are intended to not havecurrent-carrying elements. Still further, the VSD material may bepre-patterned on the target region.

Step 720 provides that the substrate is immersed in an electrolyticsolution.

Step 730 provides that a voltage in excess of the characteristic voltageis applied to the patterned region of the device. The application of thevoltage may be pulsed to occur for a designated duration of time that isless than the break-down time. The break-down time may correspond to theminimum duration in which the HAR particled VSD material is known tobreak-down when the given voltage is applied. At break-down, the HARparticled VSD material may lose its electrical characteristics,including its switching characteristics. The pattern of current carryingtraces and elements may substantially match that of the HAR particledVSD material. In the electrolytic solution, charged elements attract andbond to the exposed regions of the HAR particled VSD material, formingcurrent carrying traces and elements on the device.

In particular, one or more embodiments for electroplating onto devicesincludes using HAR particled VSD material that has reduced metallicloading through use of high-aspect ratio particles in filler material.Such formulation enables longer pulse time for performing the platingsteps of 720 and 730, as compared to conventional VSD materials.Moreover, use of HAR particled VSD material increases a likelihood thatthe VSD material will retain its integrity after the plating process.This means that the trace elements may be provided with inherentgrounding capabilities that can be integrated into the device.

Consistent with an embodiment of FIG. 7, use of VSD material inaccordance with embodiments described herein may be applied to any ofthe electroplating techniques described in U.S. Pat. No. 6,797,145.Electroplating techniques with HAR particled VSD material as describedmay be used to (i) create vias on a substrate device, (ii) multi-sidedsubstrate devices having current carrying patterns on each side, and/or(iii) interconnecting vias between multi-sided substrate devices havingcurrent carrying patterns on each side.

Other Applications

FIG. 8 is a simplified diagram of an electronic device on which VSDmaterial in accordance with embodiments described herein may beprovided. FIG. 8 illustrates a device 800 including substrate 810,component 820, and optionally casing or housing 830. VSD material 805may be incorporated into any one or more of many locations, including ata location on a surface 802, underneath the surface 802 (such as underits trace elements or under component 820), or within a thickness ofsubstrate 810. Alternatively, the VSD material may be incorporated intothe casing 830. In each case, the VSD material 805 may be incorporatedso as to couple with conductive elements, such as trace leads, whenvoltage exceeding the characteristic voltage is present. Thus, the VSDmaterial 805 is a conductive element in the presence of a specificvoltage condition.

With respect to any of the applications described herein, device 800 maybe a display device. For example, component 820 may correspond to an LEDthat illuminates from the substrate 810. The positioning andconfiguration of the VSD material 805 on substrate 810 may be selectiveto accommodate the electrical leads, terminals (i.e. input or outputs)and other conductive elements that are provided with, used by orincorporated into the light-emitting device. As an alternative, the VSDmaterial may be incorporated between the positive and negative leads ofthe LED device, apart from a substrate. Still further, one or moreembodiments provide for use of organic LEDs, in which case VSD materialmay be provided, for example, underneath the OLED.

With regard to LEDs, any of the embodiments described in U.S. patentapplication Ser. No. 11/562,289 (which is incorporated by referenceherein) may be implemented with VSD material containing a binder withconductive/semi-conductive HAR particles in filler material, inaccordance with any of the embodiments described herein.

Alternatively, the device 800 may correspond to a wireless communicationdevice, such as a radio-frequency identification device. With regard towireless communication devices such as radio-frequency identificationdevices (RFID) and wireless communication components, VSD material mayprotect a component 820 from, for example, overcharge or ESD events. Insuch cases, component 820 may correspond to a chip or wirelesscommunication component of the device. Alternatively, the use of VSDmaterial 805 may protect other components from charge that may be causedby the component 820. For example, component 820 may correspond to abattery, and the VSD material 805 may be provided as a trace element ona surface of the substrate 810 to protect against voltage conditionsthat arise from a battery event.

Any of the embodiments described in U.S. patent application Ser. No.11/562,222 (which is incorporated by reference herein) may beimplemented with VSD material containing a binder withconductive/semi-conductive high aspect-ratio particles, in accordancewith any of the embodiments described herein.

As an alternative or variation, the component 820 may correspond to, forexample, a discrete semiconductor device. The VSD material 805 may beintegrated with the component, or positioned to electrically couple tothe component in the presence of a voltage that switches the materialon.

Still further, device 800 may correspond to a packaged device, oralternatively, a semiconductor package for receiving a substratecomponent. VSD material 805 may be combined with the casing 830 prior tosubstrate 810 or component 820 being included in the device.

CONCLUSION

Embodiments described with reference to the drawings are consideredillustrative, and Applicant's claims should not be limited to details ofsuch illustrative embodiments. Various modifications and variations maybe included with embodiments described, including the combination offeatures described separately with different illustrative embodiments.Accordingly, it is intended that the scope of the invention be definedby the following claims. Furthermore, it is contemplated that aparticular feature described either individually or as part of anembodiment can be combined with other individually described features,or parts of other embodiments, even if the other features andembodiments make no mentioned of the particular feature.

1. An electronic device comprising: a layer of voltage switchabledielectric (VSD) material formed by: (i) applying a mixture to asubstrate, the mixture comprising a polymer binder, a first set ofconductor and/or semi-conductor particles, and a second set of nanoscalehigh aspect (HAR) particles other than said first set of conductorand/or semi-conductor particles; and (ii) curing the mixture on thesubstrate; wherein an amount of particles dispersed in the binder,including the first set of conductor and the second set of nanoscale HARparticles, is sufficiently low so that a percolation threshold of theVSD material is not reached.